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                筐子放球                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>小N最近在研究NP完全问题，小O看小N研究得热火朝天，便给他出了一道这样的题目：</div>
<div>有 n 个球，用整数 1 到 n 编号。还有 m 个筐子，用整数1到m编号。</div>
<div>每个球只能放进特定的两个筐子之一，第 i 个球可以放进的筐子记为 Ai 和 Bi 。</div>
<div>每个球都必须放进一个筐子中。</div>
<div>如果一个筐子内有奇数个球，那么我们称这样的筐子为半空的。</div>
<div>求半空的筐子最少有多少个。</div>
<div>小N看到题目后瞬间没了思路，站在旁边看热闹的小I嘿嘿一笑：&quot;水题！&quot;</div>
<div>然后三言两语道出了一个多项式算法。</div>
<div>小N瞬间就惊呆了，三秒钟后他回过神来一拍桌子：</div>
<div>&quot;不对！这个问题显然是NP完全问题，你算法肯定有错！&quot;</div>
<div>小I浅笑：&quot;所以，等我领图灵奖吧!&quot;</div>
<div>小O只会出题不会做题，所以找到了你--请你对这个问题进行探究，并写一个程序解决此题。</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>第一行两个整数 n，m</div>
<div>接下来 n 行，第 i + 1 行有两个整数 Ai ， Bi ，表示第 i 个球可以放的两个筐子。保证 Ai 不等于 Bi</div>
<div>1 &lt;= n，m &lt;= 2 * 10^5，1 &lt;= Ai，Bi &lt;= m</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>第一行一个整数表示半空的筐子的最小值。</div>
<p></p></p><hr/><h3>样例输入</h3><pre>4 3
1 2
2 3
1 3
1 2</pre><hr/><h3>样例输出</h3><pre>0
1，3 号球都放在 1 号筐子，2，4 号球都放在 2 号筐子。</pre><hr/><h3>提示</h3><p><p>各位不妨考虑下，如果要求输出方案应该怎么写.</p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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